Ultrasound of the Lateral Femoral Cutaneous Nerve in Asymptomatic Adults

Jiaan Zhu; Yiwen Zhao; Fang liu; Yunxia Huang; Junjie Shao; Bing Hu

Disclosures

BMC Musculoskelet Disord. 2012;13(227) 

In This Article

Discussion

Our study suggested an easier method for identifying the LFCN in volunteers using the ultrasound technique. There have been several reports about the ultrasonographic appearance of the LFCN.[10–17] Irene and colleagues[10] used the two fascial layers as the initial sonographic landmark to locate the LFCN and the mean time of identifying the LFCN was 22.5s. Bodner and colleagues[11] identified the LFCN based on the landmarks of the IL and ASIS in a cadaver and in 8 volunteers, but they did not visualize all the LFCN. Tagliafico and colleagues[15] described the technique to identify the LFCN based on the ASIS landmark in 20 patients; however, the average time for the procedure was 12 minutes. The same method was used for imaging the LFCN by Hara and colleagues[16] for ultrasound-guided LFCN blocks. Some researchers[12–14,17] reported that the most effective technique for identifying the LFCN was to search for the site at which it crossed the sartorius muscle. However, the LFCN is a very small structure that is somewhat difficult to differentiate from the surrounding soft tissues at this site, so the nerve was not observed in 30% of the cases in Damarey's report.[12] In ultrasound examinations, anatomical structures are more easily differentiated if the different tissues have greater echo differentiation on the sonogram, which is especially important for identifying tiny structures. The intermuscular space between the tensor fasciae latae muscle and the sartorius presents a hypoechoic structure, which has an echo signature quite difference from the nerve. Therefore, we recommend that the intermuscular space between the tensor fasciae latae muscle and the sartorius can be used as an initial sonographic landmark to scan the LFCN. Another reason for easier imaging of the IFCN in this study might be the use of an 18 MHz ultrasound transducer, which has a higher resolution. Based on our study results, just 7s was required to successfully identify the LFCN in all subjects, which was obviously shorter than the 22.5 seconds[10] or the 12 minutes[15] required in previous reports.

Once the LFCN was identified, the course of the nerve was then traced by scanning the structure proximally and distally. Therefore, the relationship between the LFCN and the IL was clearly observed. As demonstrated by our results, a great variability was observed not only for the nerve number but also for the relationship between the nerve and the IL. In our series, the majority of LFCNs passed under the IL and included one or two branches passing at the level of the IL. This variability is consistent with previous anatomical studies.[19,20] These findings may have potential relevance to everyday clinical surgical practice. Knowledge of the relevant anatomy is crucial before planning a surgical approach to the LFCN and in regional anesthesia when blocking the LFCN for the treatment of meralgia paresthetica.[3,4,13–16] To the best of our knowledge, there has not been a previously published study of the relationship between the LFCN and the IL using ultrasound. The morphological information will facilitate the success of procedures that involve this nerve. In this study, the distance between the LFCN and the ASIS was measured. Kosiyatrakul et al.[4] reported the distance between the LFCN and the ASIS with 7 ± 7 mm (range 1–32 mm) which was relatively shorter than our data with 15.6 ± 4.2 mm (range 2.2 - 38.7 mm). Damarey B et al.[12] reported this distance with 24 mm (range, 3–50 mm). The different measurement results might be resulted from the anatomical variation of the LFCN. Further, we also measured the CSA of the LFCN, which may be helpful in the evaluation of meralgia paresthetica.

Neuromas of the LFCN have been paid attention in previous reports,[12,21–23] and the neuromas may result from the mechanical microtraumas,[21] chronic irritation, or the role of ilio pubic tract and deep circumflex iliac artery in nervous compression.[23] However, the detection rate of neuromas in this study was lower than previously reported. This difference may be result from research subject differences.

The main limitation of this study is that verification data were not available. Another potential limitation of the study was the possibility of inaccurate nerve number counts due to the smaller diameter of the LFCN. Further studies are needed to clarify these limitations. In this study, the use of an 18 MHz ultrasound transducer allows a clear image of the LFCN, but the disadvantage is that 18 MHz ultrasound transducers are not widely used. However, we assume that this method of scanning the LFCN could also be applied using low-frequency ultrasound.

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